In the book Animal Farm by George Orwell, which animal hides during the Battle of the Cowshed and why?

True to form, it is Mollie the mare who hides during the Battle of the Cowshed. She has never been committed to—or even truly understood—the idea of the Rebellion.
When the attack that Snowball has been expected comes from the humans, Mollie wants no part of it. The other animals are alarmed after the battle not to be able to find her, thinking she might have been harmed or killed. They search for her and find her hiding in her stall, her head buried in the hay in the manger.
This is typical of Mollie. She only cares about her own needs and pleasures and can't comprehend the principle of working together for a common goal. All she wants is to have material pleasures like ribbons in her hair and sugar lumps. She will only learn the letters of her own name. She represents the lower-class, exploited individual who willingly colludes in her own exploitation—she runs away to go back to the humans—in order to have a few trinkets.